The autoxidation of pyrogallol was investigated in the presence of EDTA in the pH range 7.9–10.6.

The rate of autoxidation increases with increasing pH. At pH 7.9 the reaction is inhibited to 99% by superoxide dismutase, indicating an almost total dependence on the participation of the superoxide anion radical, O2·−, in the reaction. Up to pH 9.1 the reaction is still inhibited to over 90% by superoxide dismutase, but at higher alkalinity, O2·− -independent mechanisms rapidly become dominant.

Catalase has no effect on the autoxidation but decreases the oxygen consumption by half, showing that H2O2 is the stable product of oxygen and that H2O2 is not involved in the autoxidation mechanism.

A simple and rapid method for the assay of superoxide dismutase is described, based on the ability of the enzyme to inhibit the autoxidation of pyrogallol.

A plausible explanation is given for the non-competitive part of the inhibition of catechol O-methyltransferase brought about by pyrogallol.

https://febs.onlinelibrary.wiley.com/doi/epdf/10.1111/j.1432-1033.1974.tb03714.x

Involvement of the Superoxide Anion Radical in the Autoxidation of Pyrogallol and a Convenient Assay for Superoxide Dismutase

There is an increasing amount of experimental evidence that oxidative stress is a causal, or at least an ancillary, factor in the neuropathology of several adult neurodegenerative disorders, as well as in stroke, trauma, and seizures. At the same time, excessive or persistent activation of glutamate-gated ion channels may cause neuronal degeneration in these same conditions. Glutamate and related acidic amino acids are thought to be the major excitatory neurotransmitters in brain and may be utilized by 40 percent of the synapses. Thus, two broad mechanisms--oxidative stress and excessive activation of glutamate receptors--are converging and represent sequential as well as interacting processes that provide a final common pathway for cell vulnerability in the brain. The broad distribution in brain of the processes regulating oxidative stress and mediating glutamatergic neurotransmission may explain the wide range of disorders in which both have been implicated. Yet differential expression of components of the processes in particular neuronal systems may account for selective neurodegeneration in certain disorders.

https://science.sciencemag.org/content/sci/262/5134/689.full.pdf

Oxidative stress, glutamate, and neurodegenerative disorders

O2- oxidizes the [4Fe-4S] clusters of dehydratases, such as aconitase, causing-inactivation and release of Fe(II), which may then reduce H2O2 to OH- +OH.. SODs inhibit such HO. production by scavengingO2-, but Cu, ZnSODs, by virtue of a nonspecific peroxidase activity, may peroxidize spin trapping agents and thus give the appearance of catalyzing OH. production from H2O2. There is a glycosylated, tetrameric Cu, ZnSOD in the extracellular space that binds to acidic glycosamino-glycans. It minimizes the reaction of O2- with NO. E. coli, and other gram negative microorganisms, contain a periplasmic Cu, ZnSOD that may serve to protect against extracellular O2-. Mn(III) complexes of multidentate macrocyclic nitrogenous ligands catalyze the dismutation of O2- and are being explored as potential pharmaceutical agents. SOD-null mutants have been prepared to reveal the biological effects of O2-. SodA, sodB E. coli exhibit dioxygen-dependent auxotrophies and enhanced mutagenesis, reflecting O2(-)-sensitive biosynthetic pathways and DNA damage. Yeast, lacking either Cu, ZnSOD or MnSOD, are oxygen intolerant, and the double mutant was hypermutable and defective in sporulation and exhibited requirements for methionine and lysine. A Cu, ZnSOD-null Drosophila exhibited a shortened lifespan.

Superoxide Radical and Superoxide Dismutases

The reactive superoxide radical, O2-, formerly of concern only to radiation chemists and radiobiologists, is now understood to be a normal product of the biological reduction of molecular oxygen. An unusual family of enzymes, the superoxide dismutases, protect against the deleterious actions of this radical by catalyzing its dismutation to hydrogen peroxide plus oxygen.

https://science.sciencemag.org/content/sci/201/4359/875.full.pdf

The biology of oxygen radicals

The hypothesis that dopamine is important for reward has been proposed in a number of forms, each of which has been challenged. Normally, rewarding stimuli such as food, water, lateral hypothalamic brain stimulation and several drugs of abuse become ineffective as rewards in animals given performance-sparing doses of dopamine antagonists. Dopamine release in the nucleus accumbens has been linked to the efficacy of these unconditioned rewards, but dopamine release in a broader range of structures is implicated in the 'stamping-in' of memory that attaches motivational importance to otherwise neutral environmental stimuli.

Dopamine, learning and motivation

https://www.jbc.org/content/249/8/2447.full.pdf

The generation of hydrogen peroxide, superoxide radical, and hydroxyl radical by 6-hydroxydopamine, dialuric acid, and related cytotoxic agents.

Studies on the distinction between uptake inhibition and release of (3H)dopamine in rat brain tissue slices.

Superoxide dismutase inhibited the autoxidation of 6-hydroxydopamine as measured by the rate of formation of a quinone and the rate of oxygen consumption. These observations demonstrate the formation of the superoxide radical during the autoxidation process. This finding may be relevant to the mechanism of adrenergic nerve terminal degeneration caused by 6-hydroxydopamine.

6-Hydroxydopamine: Evidence for Superoxide Radical as an Oxidative Intermediate

The developing neostriatum of the rabbit: Correlation of fluorescence histochemistry, electron microscopy, endogenous dopamine levels, and [3H]dopamine uptake

Hydrogen peroxide, dialuric acid, or 6-hydroxydopamine inhibited the uptake of dopamine, norepinephrine, and serotonin into rat brain synaptosomal preparations. The addition of catalase protected all systems, but catalase was only partially protective for 6-hydroxydopamine acting upon catecholamine uptake. The data show that 6-hydroxydopamine generates hydrogen peroxide and that hydrogen peroxide can damage the biogenic amine uptake systems. Part of the damage caused by the 6-hydroxydopamine that accumulates in the catecholamine nerve terminals in vivo may be attributed to the hydrogen peroxide.

https://science.sciencemag.org/content/sci/172/3989/1257.full.pdf

Richard E. Heikkila

Papers

The generation of hydrogen peroxide, superoxide radical, and hydroxyl radical by 6-hydroxydopamine, dialuric acid, and related cytotoxic agents.

Studies on the distinction between uptake inhibition and release of (3H)dopamine in rat brain tissue slices.

6-Hydroxydopamine: Evidence for Superoxide Radical as an Oxidative Intermediate

The developing neostriatum of the rabbit: Correlation of fluorescence histochemistry, electron microscopy, endogenous dopamine levels, and [3H]dopamine uptake

Inhibition of biogenic amine uptake by hydrogen peroxide: a mechanism for toxic effects of 6-hydroxydopamine.